The main structural components of modern aircraft are the fuselage; wings; empennage, or tail surfaces; power plant; and landing gear, or undercarriage. The fuselage is the main body structure to which the wings, tail, landing gear, and power plants are attached. It contains the cockpit or flight deck, passenger compartment, cargo compartment, and-especially in the case of fighter aircraft--the engines and fuel tanks.
The wing is the most important lift-producing element of an aircraft. Wing designs vary, depending on the aircraft type and purpose. Propeller-driven aircraft normally have an all-metal straight wing with a thick camber, or curvature. Jet transports have swept-back wings of medium camber that lower aerodynamic drag and improve performance at high airspeeds. Both straight and swept-wing aircraft normally have ailerons attached to the outermost trailing edges of the wing. These ailerons raise and lower in opposition to one another, to increase or decrease lift on their respective wing in order to facilitate turning the aircraft. The wing also has flaps along the trailing edge, inboard of the ailerons. Flaps increase aerodynamic lift and drag and are used during takeoff and landing to increase lift at low speeds. Modern swept-wing transport aircraft also have high lift devices called leading-edge slats, which extend in conjunction with the flaps to further increase the lifting capability of the wing.
The conventional type of tail assembly consists of two basic surfaces, horizontal and vertical, each of which has movable sections contributing to control of the craft and fixed sections to provide stability. The leading section of the horizontal surface is known as the horizontal stabilizer, and the rear movable section, as the elevator. The stationary section of the vertical surface is called the fin, and the movable section, the rudder. Two vertical surfaces are used in some aircraft; in that case, a double rudder is used. The V-shaped tail combines the rudder and elevator functions in a single device.
Tails vary in size according to the type of aircraft, but in supersonic flight the tail should be as small as possible. Its complete elimination would be the ideal design. This has led to the delta wing and similar designs, in which there are no horizontal tail surfaces. Instead, the wing trailing edge control surfaces can act together to adjust aircraft pitch in the same way as the elevators, and can also act opposably to bank the aircraft. Such surfaces are called "elevons".
The first powered, controllable aircraft, Orville and Wilbur Wright's flying machine, demonstrated in its structure the same basic principles of flight as do today's high-flying jets. The wings, or airfoils, of the original 1903 Wright Flyer resembled a box kite. A small pair of wings, called a canard, was located forward of the main wings and provided control about the pitch axis, allowing the aircraft to climb or descend. The canard performed the same function as the elevators that are attached to the horizontal stabilizers on most modern aircraft or the elevons on delta wing aircraft.
Aircraft that can fly faster than the speed of sound, have been used by the military for many years. Commercial supersonic aircraft (SuperSonic Transports, or SSTs) have been limited to the Concorde, built by the British and French in the 1960's (first flight in 1969), which has proved to be a commercial failure in large part because of the vast amounts of fuel it consumes. The Russians have also built an SST, the TU-144 (known in the west as the "Concordski"), but it was not a successful design and was withdrawn from service after several disastrous crashes.
One of the main drawbacks of the SST design is that it must be optimized for high-speed flight in order to reach supersonic speeds. It has been discovered that the best shape for optimum cruise at Mach 2 is a slender straight edged delta twice as long as its span. The "ogival" wing form used on the Concorde (see FIG. 1) is an attempt to modify the optimum delta for greater efficiency at low speeds, particularly at take-off and landing. Despite this, the Concorde shows very high fuel consumption and low lift at low altitude and speed, and requires a very long take-off roll. Similarly, the very "slippery" shape requires a very long landing roll due to high landing speeds and low drag. The prototype Concorde even used a parachute to aid the brakes in landing, and such devices are common in military aircraft.
In order to gain lift for takeoff, the wing must be raised to a higher angle of attack (angle of the wing relative to the airflow over the wing) than it has on the runway. This is known to pilots as "rotation", when the nose is raised to increase lift for takeoff. In order to rotate the aircraft in the normal aircraft design, the elevators are angled trailing-edge-upward to exert a downward force at the rear of the fuselage. This raises the nose, but at the cost of a downward force on the aircraft just when the aircraft most needs all the lift it can muster.
The solution to this problem is the canard--the same tail-first design idea that the Wright Brothers used. The canard wing exerts an upward force at the front of the aircraft, increasing the total lift available while rotating the aircraft. The canard, if its angle of attack is properly set, can also reduce the likelihood of a catastrophic full-power takeoff stall by stalling before the main wing stalls, lowering the nose of the aircraft.
This design has been popularized by such designers as Burt Rutan (the VariEze, Voyager, and others), and is currently being commercially produced in the Beechcraft Starship. Some supersonic delta-wing designs have used canards. An early supersonic bomber, the B-70 Valkyrie, is an example of this, as is the SAAB Viggen fighter made in Sweden.
However, just as the canard is advantageous at low speeds, it is disadvantageous at supersonic speeds. At those speeds lift is abundant even at low angles of attack and small wing areas and thickness, but drag is an overwhelming problem.
As far as landing is concerned, the SST needs all the help it can get to slow down from its high landing speeds. Parachutes are not really useful in commercial applications, leaving the thrust reversers and wheel brakes to do the job.